Hello people of Honda Tech. I'm new to this site and appreciate any help or advice I receive. I have a 1991 Honda Accord that failed the

emissions portion of the CA SMOG test. I'm a DIYer and understand a fair amount about automobiles.

First thing I've done since the fail is an oil change(it needed it bad), checked air filter(ok), checked plugs and wires(ok), timing(ok), main

relay(ok), cooling system(ok), cap rotor and coil has some wear so these items will be replaced. HC and NO were above the MAX amount.

Everything else passed. Here are the numbers:

HC: 15mph-MAX 83- MEAS 166/ 25MPH-MAX 65- MEAS 151_______NO: 15MPH-MAX 559- MEAS 426(OK)/ 25MPH-MAX 516- MEAS 568


The car bogs out sometimes almost like a miss fire, but runs smoothly after I ease up on the throttle. Maybe this contributes to the FAIL. I

don't know?

I have one free retest and would like not having to buy a new vehicle. Hopefully I can get it to pass! Any suggestions...? Thank you much.

 

I would replace the O2 sensor, reset the ECU by pulling both fuses (one under the hood, the other in the cabin on the driver's side), replace the cap and rotor as you suggested, and set the timing again. The O2 sensors are notorious for failing without throwing a code. My 91 Accord Aero Deck barely passed TX emissions this year, and I have replaced everything except the cap (that is coming in tomorrow). Good luck.

 

HCs are a terrible way to judge how a car is running, too lean or rich and HCs will increase, it's a 'U' on the graph.

NOx is a decent indicator, but it can be affected by EGR function, ignition lead, changes in compression ratio, etc.

If you can post the other three gasses of CO, O2 and CO2.

Off the cuff, your car probably has over 100K miles, and there has never been any maintenance done on the EGR system. Ports are blocked causing a lean misfire which creates excessive HCs from unburnt gases and high NOx readings from malfunctioning EGR system, which is causing a lean misfire.

Check the FAQ at the top of the forum on how to clean out your 90-93 Accord intake. Your intake will require removal of port plugs(can be seen on the runners of the intake) so as to clean each port of soot.
Removal of just the main EGR manifold plugs will only clear out the main port, this will not do much as the main culprit is usually the port/passage between EGR manifold port and intake runners.

 

MAD_MIKE is 100% right about the EGR ports. You can buy the new port plugs at the Honda dealer. It is not that difficult to get done. When I popped mine off the number 1 port was completely plugged, and the others were restricted.

 

Bondo sells the perfect dent puller/slide hammer to use in conjunction with a drill. Drill a hold slightly smaller than the dent puller screw. Screw the screw in after attaching it to the dent puller and then just pop the plug out.